Interaction of nanoparticles with non-spherical micelles and bilayers

Abstract

Interaction of different-sized anionic silica nanoparticles with non-spherical micelles and bilayers of non-ionic surfactant C12E10 has been studied by small-angle neutron scattering (SANS). The non-ionic surfactant C12E10 in aqueous solution self-assembles to form core–shell spherical micelles. Different means (temperature, salts, and alcohols) have been examined to induce the structural transition of micelles from spherical to non-spherical and bilayer formation. The dehydration from micellar shell leads to such transition in the cases of increasing temperature and selective salt (e.g., KF). On the other hand, for alcohols, spherical to non-spherical micellar transition or bilayer formation arises for long-chain length alcohols CnOH ( n > 5) because of the mixed micelles formation of alcohol with surfactant. From the different ways to alter the micellar morphology, transitions obtained by alcohols were found to be the best suited for nanoparticle–surfactant solution as they do not influence the interactions between nanoparticle and surfactant and among nanoparticles. It is found that the shorter chain length alcohols (CnOH, n ≤ 5) interact with nanoparticles via the adsorption of individual micelles while the non-spherical micelles and bilayers of surfactant formed in the presence of long-chain length alcohols rearrange themselves to attach onto the nanoparticles. SANS with an advantage of contrast variation (contrast matching silica nanoparticles with solvent) provides the evidence of bilayer formation around nanoparticles. The concentration effect of long-chain length alcohol on micelle morphology and subsequently on the nanoparticle–surfactant system is also examined. It is found that the adsorption of surfactant bilayer structures is prominent in the case of larger particle size due to flattened curvature.